Dragline propulsion apparatus



June 10, 1969 R s, PETERSON ET AL 3,448,819

DRAGLINE PROPULS ION I APPARATUS Filed April 20, 1967 Sheet & of 2 SHOEST B TUB RAISED SHOES LIFTING OFF THE GROUND LOWER'NG FROM THE I TO THETO THE LOAD TORQUE MOTOR SPEED MOTOR SHUNT FIELD STRONG I c WEAK I WEAKI d I I IOO IOO I |oo% 1 REFERENCE TO THE REGULATOR 50% I FIG. 3.

FIG.5.

United States Patent Office 3,448,819 Patented June 10, 1969 3,448,819DRAGLINE PROPULSION APPARATUS Robert S. Peterson and Darl C. Washburn,Jr., Williamsville, N.Y., assignors to Westinghouse ElectricCorporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Apr.20, 1967, Ser. No. 632,344 Int. Cl. B62d 57/02, 51/06 US. Cl. 180-8 12Claims ABSTRACT OF THE DISCLOSURE A system for electrically controllingand synchronizing the walking movement cycle of a dragline with no rigidConnecting shaft between the walking shoes. A Signal, proportional tothe difference in angular displacement of the walking shoes, is used inan additive sense to boost the movement of the lagging shoes and in asubtractive sense to buck the movement of the leading shoe until propersynchronization is achieved.

Field of the invention This invention relates generally to walkingdraglines, and more particularly, to an improvement in the propel lingof draglines employing walking shoes or pontoons.

Description of the prior art Walking dragl-ines for open-pit mining haveincreased in size tremendously over the past few years. They move bywalking on pontoons similar to the way a human being walks on crutches.The pontoons (feet) are rigidly connected to a leg which is turn isdriven through an eccentric by a drive shaft. There are two feet, one oneach side of the dragline, which are rotated in synchronism as thedragline walks. In order to improve synchronism, a mechanical shaft hastraditionally connected the two feet. This shaft may be as large as 90feet long and 3 feet in diameter; moreover, the shaft size demands thatit be designed in sections with expensive couplings and bearingsutilized between the shaft sections.

In operation the shaft is geared to DC drive motors. Generally, an evennumber of motors is used for the walking motion and the shaft becomes amere timing device not transmitting any torque from one side to theother. However, on uneven ground, an unbalanced loading on the pontoonscan cause transmission of power from one end of the shaft to the otherend and, if the shaft is not designed to transmit this torque, it maybreak. In addition to the expense connected with replacing the shaft,the dragline would ,be inoperable over a significant period of time.Therefore, it would be a significant advantage if this connecting shaftcould be removed yet still maintain proper synchronism between the twopontoons. The immediate result would be a substantial savings in space,weight, and dollars.

Summary of the invention It is therefore, a general object of thepresent invention to provide a new and improved dragline walking system.

A further object of the present invention is to provide a new andimproved walking dragline whereby the dragline propel shaft is replacedby an electrical tie.

A still further object of the present invention is to provide a new andimproved dragline propel system whereby on uneven ground, the walkingshoe (foot) touching the higher ground first will stay in that positionuntil the other walking shoe reaches the ground.

Yet, a further object of'the present invention is to provide anelectrically controlled propel system for a drag line whereby theangular position of the walking shoes (feet) are substantially equalregardless of the ground slopc.

A still further object of the present invention is to provide anelectrically controlled propel system whereby the torque for anyspecific angular position -of the crank arms driving the walking shoesmay vary, depending on the slope of the ground upon which the draglineis operating.

A still further object of the present invention is to provide animproved dragline walking system whereby the mechanical stresses on thecab and frame structure are substantially reduced from the stressesnormally present with a rigid propel shaft. 1

In general the present invention relates to a system for cyclicallycontrolling, in synchronism, the running speeds of the DC drive motorsthat independently drive the separate shoe (foot) operating cranks of aself-propelled dragline shovel. Use is made of a variable speedreference to control thejgaverage rotational speed of the shoe cranks.The mechanically separate motor driven propel cranks for the shoes aretied to the common reference through a Synchrotie system which comparesthe positions of the respective cranks and generates separate errorsignals for correcting the deviation of each shoe crank from theiraverage position. The speed of the cranks is controlled during differentparts of the 360 cycle to effect slow movement on the power portion ofthe cycle and speed-up during the recovery portion of the" cycle, with acushioning transition from the speed of the recovery cycle at a pointjust before the power impact. Speed and torque are regulated throughfeedback loops.

The objects of our invention hereinbefore recited are merelyillustrative. Other objects and advantages will become more readilyapparent from a study of the following specification when made inconjunction with the accompanying drawings.

Description of the drawings propel system synchronization control usingLaplace transforms.

Descriptioln 0f the preferred embodiment Referring to FIG. 1, numeral 1denotes the cab and frame structure of the dragline. The cab is mountedon a supporting frame structure 2 which is rotatable on a A circularrail 3. The rail is carried by a tub 4 of cylindrical shape. 1

In order to move the shovel along the ground, a walking arrangement isprovided which includes two walking pontoons (feet) 10 arranged atopposite sides ofth'e cab and frame structure 1. Each pontoon 10 isattached to a walking structure member 12 which is in turn connected toa crank 14. A beam 15 is attached from a freely' rotating point on thecab 16 to a freely rotating point on the walking structure member 12.There is no mechanical linkage or tie between the rotating cranks 14 oneach side of the tub 1.

During a walking cycle, propel motors rotate the crank in the clockwisedirection. As a result, the walking structure member 12 and the pontoons10 are moved toward the righthand side of the illustration until thepontoons reach ground as indicated by the Diagram A. Thereafter, whilethe cranks continue to rotate in a clockwise direction, the pontoonsexert pressure against the ground and cause the tub 4 and hence theentire machine to be lifted vertically with the lifting motion beginningat the rear of the machine as shown in Diagram B. As the cranks 14continue to rotate in a clockwise direction, as shown in Diagram C, thepontoons impart a horizontal motion to the machine towards the rear asindicated by arrow 20. As a result, the front end of the tub 4 isdragged over the ground a distance d. At the end of a walking cycle, thepontoons 10 are lifted olf the ground as the respective cranks 14continue to move in a clockwise rotation. The pontoons come to rest asshown in Diagram D where they are idly suspended from their respectivecrank arms; further motion can be achieved by performing additionalwalking cycles. The cranks 14 are considered to be in'phase with eachother when the pontoons 10 are in step (i.e., in phase) with each other.

In the movement of the dragline over the ground, it is imperative thatthe walking shoes or pontoons by synchronized to a significant extent.With no connecting shaft between the two cranks driving the walkingshoes, the design of the control equipment in achieving a predeterminedmode of operation becomes significant. In this regard, the principles ofthe present invention are designed to meet minimum specific requirementsfor pontoon synchronization as given below:

(1) The crank arm position error should not exceed :5 during any walkingcycle.

(2) Shoes and tub should accelerate together with a position error notexceeding i5% (3) If one side of the dragline is stalled due to externalloading, the other side should remain within 15 without creating anyabnormal effects or damage to the mechanical equipment.

(4) All motors should have proper current limit protection.

(5) On uneven ground, the shoe touching the higher ground first shouldremain in that position until the other shoe touches the ground. Thus, anecessary error in shoe positions should exist to compensate forunevenness of the ground. This error generally should not exceed FIGURE2 presents a diagrammatic representation of the propel system withpontoon synchronization control. A master switch 20 is provided to givea reference or command signal for setting the proper speed with whichthe walking cycle should occur. This input reference signal is fed to apropel regulator 22 which acts as a voltage controller until currentreaches certain predetermined limits at which time the regulatoroperates as a current controller. In effect then, the regulator 22operates as a parallel control for both voltage and current. A furtherand. more complete description as such a parallel controller is given incopending patent application Ser. No. 597,010 entitled Limit of Rate ofRise of Current in a Parallel Control Scheme and filed Nov. 25, 1966 byHermann Eisele and assigned to the same assignee as the presentinvention. Output from the propel regulator 22 is fed to a poweramplifier having a high gain and providing a signal to the summingjunctions 2 and E The summations of signals at summing junctions 2 and Eare passed on respectively to coils C and C to energize respectively thegenerators G and G Generator voltage is then directed to respectivepropel motors PM and PM which operate respective synchro devices SY andSY through associated gear mechanisms such that each synchro will onlycomplete a single turn for each walking cycle. For purposes of theillustration only one motorgenerator set is shown for each pontoon;however, in practice, it would probably be necessary to energize aplurality of motor-generator sets for each pontoon. The angulardisplacements of the synchros 0 and O are fed to a synchro-tie errordetector E which generates a position error signal a which is fed to asynchronizing controller 30. The synchro-tie error detector E comparesvectorially the voltages 0 and 0 from the synchros SY and SY to producethe output signal 0 which is proportional to error position. For a moredetailed description, reference should be made to Patent No. 3,086,153,entitled Synchronized Conveyor Control by G. E. Mathias et al. andassigned to the same assignee as the present invention. An output signalfrom the synchronizing controller 30 is then fed to a power amplifier 32which has considerably less gain than power amplifier 24. Output fromamplifier 32 is less than added to the regulator module output on oneside and subtracted from the regulator module on the other side.

The generator voltages from G; and G are detected respectively byvoltage sensors VS and VS which provide signals to a summing amplifier34. The summing amplifier 34 then averages the two signals and therebyprovides a feedback signal V to the propel regulator 22. Armaturecurrents from the propel motors PM and PM which drive the pontoons aremonitored through shunt circuits S and S respectively and measured bycurrent sensors CS and CS The sensors feed the current from each sideinto a switching circuit 40 whose output I corresponds to the higher ofthe two current inputs. The output l is then used as current feedback tothe regulator 22.

Generally, the circuit of FIG. 2 operates such that a reference voltageprovides an energizing signal for operation of the walking pontoonswhich under normal circumstances will be synchronized, i.e. be in stepwith each other. At such times when the pontoons may be out ofsynchronization an error signal indicating the position error is fedback to the energizing circuits which correct for this position.Meanwhile, the approximate speed of operation of both pontoons is sensedand compared to a reference; lack of correspondence with this referencevoltage will then set up a compensating signal which will tend to drawthe actual operating characteristics close to the reference signal.

Referring now to FIG. 3 and by way of example, typical operatingcharacteristics of the crank arm position in degrees is shown withrespect to various operating parameters. For each walking cycle thecrank arm moves 360. During the first 113 the walking shoes or pontoonsare being lowered to the ground. From 113 to 208 the pontoons arepushing against the ground to lift the tub off the ground; from 208 to267 the tub is lowering back to the ground level. The final portion ofthe cycle, from 267 to 360 merely lifts the pontoons from the groundback to their original starting position where they are hanging idly atthe sides of the tub.

The motor speed which is used to control the rate of change of the crankarm position is shown in curve B of FIG. 3. During the first 113 whilethe pontoons are lowering to the ground it as advantageous that thecrank arm move relatively quickly; however, as the shoes near the groundit is advisable that the speed at which the come into contact with theground be considerably slowed to elminiate any sudden jolting. Duringthis portion of the' walk cycle there is essentially no load on themotor since there is no resistance to the movement of the shoes from theidle position to the ground position as seen load torque curve in curveA. During this period the motor shunt field remains weak until adecrease in speed is necessary as the shoes near the ground whereuponthe field increases as shown by curve C. Curve D indicates that thereference to the regulator remains 100% until just before the shoestouch the ground whereupon the reference drops to since the motor speedis decreased.

During the second portion of the walking cycle where the tub is liftingoff the ground the load torque suddenly increases as shown by curve A.Load torque continues to increase slightly until a maximum is reachedwhen the tub is furthest from the ground. Fromthen on, as the cycleshifts away from maximum lift, load torque rapidly falls off as theweight of the machine itself contributes heavily to lowering. Meanwhile,the motor speed initially causes a return to 100% reference to theregulator.

During the third portion of the walking cycle where the tub is lowering,the load torque moves from 0 to negative as the gravitational force ofthe tub and cab and frame structure generates most of the loading force,as

shown by curve A. In the meantime the motor speed remains constant to aposition near where the tub will touch the ground at which time themotor speed is gradually decreased to a minimum Speed such that the tubmay be gently set upon the ground again. The motor shunt field remainsstrong throughout the tub lowering to provide braking and the referenceto the regulator generally follows the motor speed curve reaching aminimum at a point just before the tub actually touches the ground.Should there be different ground levels for the pontoons, the loadtorque curve for each during the raising and lowering of the tub wouldnot be coincident; the pontoon reaching the ground last would thenfollow the dashed portion of curve A.

The last portion of this cycle where the shoes are lifted from theground to their idle position requires only a minimum of load torque.And once the shoes have left the ground they can rapidly return to theiridle position as shown by the quick increase of motor speed in curve B.With no load the motor shunt field again becomes quite weak and theincreased speed means that a 100% reference to the regulator can againbe used.

It should be noted that curve D, reference to the regulator, may beachieved either by an operator manually changing reference during therespective portions of the cycle as indicated by a curve or preferably,it may be done automatically by a system of contacts and relays.

The block diagram of FIG. 4 presents a mathematical model using Laplacetarnsforms for the synchronizing control loops in the system shown inFIG. 2. A reference voltage V is fed to the regulator 22. A signaloutput from the regulator is separated at terminal 6 to be fed to eachof the summing junctions 2 and E Output from the respective summingjunctions are then fed to the generators which have a transfer functionof where T is the generator time constant. The respective m and ax arein radians per second. Feedback from the respective motors is returnedrespectively to summing junction 2 and E The speed of the respectivemotors a 40 and aw is then fed through transfer functions i as and

to summing junction 2 at which point the relative angular generatorvoltages V and V are fed back by a factor of one-half to the regulator22. The generator voltages as applied to summing junctions 2 and 2 drivethe propel motors which have a transfer function of where T is thearmature time constant. The motors are connected respectively throughgear mechanisms having a transfer function,

where T is the mechanical time constant. Input voltages at junctions Zand E consist of two components, motor torque i R and load torque z' R iR where R is is armature resistance, 1',, is armature current, and i andi are armature load currents. Output from the gear mechanism transferfunction then provides signals representative of speeds a and aw where ais the voltage constant of the motor in volts per radian per second andpositions 0 and 0 of the crank arms are determined. The angulardifference between 0 and G is then transferred to the synchronizingcontrolled 30 which has a transfer function of where T and T arerespective lead and lag time constants of the synchronizing controller.The synchronizing controller 30 is a lag-lead controller designed so asto cancel the generator time constant T with the lead time constant Tand to make the lag time constant be as small as practical depending onthe selection of components to meet other requirements such ascontrolled gain and lead time constant T Output from the synchronizingcontroller is then fed to junction 6 whereupon it is sent to eithersumming junction E or is changed in polarity and fed to summing junction2 This signal acts along with the reference input to provide anenergizing signal for the respective generators.

If the leadtime constant of the synchronizing controller T i sset equalto the time constant of the generator T then the following expressionfor the crank arm error position (6 0 can be obtained from the diagramof FIG. 4.

where:

a=voltage constant of the motors I I =armature load current c th gs K=controller 3-0 gain in volts/radian K =amplifier 32 gain involts/radian K =generator gain and I =generator field amps for stallcurrent 1 R =generator field resistance in ohms I =stall current tar nR.

Normalizing the above equation gives the following:

where M is the maximum allowable error in radians. The worst conditionoccurs when one side crank arm is stalled and the other side is free torotate. Under this condition we have the following:

While our invention as described in the foregoing refers to walkerdrives of draglines, it will be understood that the principle and meansare also adaptable to walking equipment if used in connection with otherthan draglines and that the invention can be used to advantage wherevera hoisting machine or shovel operates in accordance with the speed andtorque cycle which involves load variations similar to those discussedin the foregoing.

We claim as follows:

1. A synchronizing system for operating a pair of walker-type mechanismseach including a foot operable through a predetermined walking cycle androtatable propulsion means coupled to the foot, each foot having acorrelative pos tion within said walking cycle for any given angularposition of its associated rotatable propulsion means, said respectiverotatable propulsion means being mechanically independent of each other,said synchronizing system comprising:

variable reference means providing a reference signal for settingdesired operation for said walker-type mechanisms, first and seconddrive means, each for driving a difierent one of said rotatablepropulsion means,

regulat ng means responsive to said reference signal and PI'OVldll'lg acorresponding drive signal for each of said drive means for the controlthereof,

controller means responsive to the positions of said walker-typemechanisms for providing compensating signals to each of said drivemeans proportional to the relative difference in angular displacement ofsaid walker-type mechanisms, and

feedback means responsive to at least one electrical operatingcharacteristic of each of said drive means to provide correction signalsto said regulating means.

2. The synchronizing system as set forth in claim 1 wherein saidcontroller means includes error signal providing means for developing anerror displacement signal proportional to the difference in angulardisplacement of said walker-type mechanisms, and a synchronizingcontroller responsive to said error displacement signal to provide asubtractive compensating signal to the leading drive means and anadditive compensating signal to the lagging drive means.

3. The synchronizing system as set forth in claim 1 wherein saidfeedback means includes:

first condition sensing means to detect the level of a first electricalcondition relative to each said drive means to provide a first conditioncorrection signal to said regulating means, and

second condition sensing means to detect the level of a secondelectrical condition relative to each said drive means to provide asecond condition correction signal to said regulating means.

4. The synchronizing system as set forth in claim 3 wherein said firstcondition is drive speed and said second condition is drive torque.

5. The feedback means as set forth in claim 3 wherein said firstcondition is generator voltage and said second condition is armaturecurrent.

6. The synchronizing system as set forth in claim 3 wherein said secondcondition sensing means provides a feedback signal equivalent to thehigher one of the levels of said second condition of the respectivefirst and second drive means.

7. In a vehicle provided with at least a pair of walking pontoons andmechanically separate rotatable propulsion members for operating saidrespective pontoons, the combination of drive means including a motorcoupled to each of said rotatable propulsion members, synchronizingmeans operative with said drive means and responsive to the differencebetween the angular positions of said rotatabel propulsion members forsynchronizing the angular displacement of said rotatable propulsionmembers within predetermined limits, and feedback means responsive to anelectrical characteristic of said drive means for affecting theoperation of the drive means.

8. The combination as set forth in claim 7 wherein said synchronizingmeans includes: detector means for detecting the relative difference inangular displacement of said rotatable propulsion members to provide anerror signal proportional to said angular displacement, and controllermeans responsive to said error signal for providing an additive signalto the drive means of the lagging rotatable propulsion member and asubtractive signal to the drive means of the leading rotatablepropulsion member until said rotatable propulsion members aresynchronized in a predetermined manner.

9. The synchronozing system as set forth in claim 2 wherein saidfeedback means includes:

first condition sensing means to detect the level of a first electricalcondition relative to each said drive means to provide a first conditioncorrection signal to said regulating means, and

second condition sensing means to detect the level of a secondelectrical condition relative to each said drive means to provide asecond condition correction signal to said regulating means.

10. The synchronizing system as in claim 3 wherein:

each of said drive means includes a motor having an armature coupled tosaid rotatable propulsion means associated with that drive means and apower supply source responsive to said regulating means for energizingthe motor,

said first condition is power supply source output voltage, and

said second condition is armature current.

11. In a vehicle provided with first and second walking pontoons andfirst and second mechanically separate rotatable propulsion member foroperatng the first and second pontoons respectively, the combination offirst and second drive means for respectively driving said first andsecond propulsion members, each said drive means including a motorcoupled to the propulsion member associated with that drive means,regulating means responsive to a control force for supplying similardrive signals to the first and second drive means for the controlthereof, synchronizing means operative with the first and second drivemeans and responsive to phase difference between said propulsion membersfor forcing said pontoons toward synchronism, and means for supplyingfeedback from both said drive means to said regulating means formodifying the output of the regulating means, said feedback relating toat least one kind of electrical characteristic.

12. The combination as in claim 1'1 wherein said synchronizing meansincludes means for detecting the phase difference between said rotatablepropulsion members to provide anerror signal proportional to said phasedifference, and means responsive to said error signal for providing anadditive signal to the drive means of the lagging rotatable propulsionmember and a subtractive signal to the drive means of the leadingrotatable propulsion mem- 9 10 her until said rotatable propulsionmembers are synchro- 2,469,140 5/ 1949 Wahlberg 318-85 nized in apredetermined manner. 3,267,345 8/1966 Boening 318-52 3,366,192 1/1968Le Tourneau 180-8 References Cited UNITED STATES PATENTS 5 LEO FRIAGLIA,Prz'mary Exammer. 2,380,431 7/1945 'I-Iardin-g et a1. 1808 U.S. C1.X.R.

2,399,417 4/1946 Wilson et a1. 1808 31885

